A 3D image sensor called light detection and ranging (LIDAR) or laser detection and ranging (LADAR) is a system that may catch the reflected light energy from a target after emitting a pulsed laser light with a light detection element, convert the light energy into an electrical signal and thus calculate a distance to the target or the moving speed of the target.
A LIDAR system is being widely applied to various fields such as a sensor for detecting a forward obstacle of a robot or unmanned vehicle, a laser gun for measuring a speed of a moving object, an airborne geo-mapping device, 3D terrain scanning device, underwater scanning device, etc.
Recently, the application field of the LIDAR system is being expanded to an advanced driver assistance system that warns a driver or reduces the speed of a vehicle if an emergency situation due to a forward obstacle or a side obstacle occurs, or to an autonomous driving system such as an unmanned ground vehicle or tractor.
In order to apply a LIDAR system for recognizing the forward environment of a vehicle, unmanned tractor, or robot that runs at a high speed, it is needed to obtain 3D dense point cloud information that has a wide field of view.
As a technology for obtaining 3D point cloud data of a wide field of view, US patent publication No. 2010-0020306 discloses a high definition LIDAR system that consists of plenty of laser diodes, multiple detectors (or a single detector) detecting the reflected and retuned beam, a housing fixed with above photo elements and lenses, and a rotary unit rotating the housing through 360 degrees at a high speed.
The entire group of the multiple laser diodes that are arranged in the LIDAR system are arranged at different angles and thus laser beams are to be spread at a certain vertical angle, such as 40 degrees. Thus, it is possible to obtain point cloud data on x, y, and height, such as 3D data.
In addition, the system includes a first assembly that is installed in a horizontal direction in order to obtain appropriate data related to height, and a second assembly that is arranged at a slight downward angle as compared to the first assembly. The first assembly obtains long-distance point cloud data as compared to the second assembly, and the second assembly may obtain information around a running vehicle, such as short-distance point cloud data, due to an angle arrangement.
In case of the first assembly, in order to obtain point cloud data on a long distance, it is needed to increase the laser output power, accordingly which leads to drawbacks in that the volume of a whole sensor increases and the cost of a unit sensor rises.
Moreover, since the space between point cloud data becomes larger as a distance becomes long, the LIDAR system has a drawback in that a point cloud data obtained from a long distance object has low vertical resolution and thus the reliability of its processed data also decreases. Most of all, since 32 or 64 laser diodes are individually installed, emission angles are different and thus it is difficult to precisely calibrate a laser diode and a corresponding photo detector individually.
Moreover, since a general 3D laser scanning system has a structure in which both a laser source and a light transmitting/receiving unit are installed and rotated in a rotation-driving device, a rotary motor having great capacity is needed due to the weight of a laser source and a cooling structure for cooling the laser source and thus there are drawbacks in that the manufacturing cost of a scanning system increases and its volume increases as well.